Search

The nano-sized metal oxides (MOs) as combustion catalysts have been widely employed in solid rocket propellants, but the functionality of these materials is greatly restricted owing to their agglomeration. The catalytic activity of MOs on nanoscale was found to be significantly improved by the incorporation of MOs with carbon nanomaterials, which normally act as carriers allowing for well-distribution of MOs. In this paper, the CuO and Fe2O3 nanoparticles were produced by hydrothermal method and the CuO@C and Fe2O3@C nanocomposites with a uniform structure have been fabricated by an in-situ growth of corresponding MOs on the porous activated carbon (pAC). The morphology of the prepared MOs nanoparticles and resultant pAC carried ones were characterized using scanning electron microscope. It has been shown that the CuO and Fe2O3 nanoparticles are tightly adhered and dispersed on the surface of pAC. Their catalytic effects on the thermal decomposition of hexogen (RDX) were analyzed using thermal analysis techniques. Results indicate that the thermal decomposition of RDX was considerably promoted in the presence of these catalysts, where the CuO@C and Fe2O3@C were found to be capable of lowering the Tp for RDX by 14.8 °C and 12.4 °C, respectively. In addition, the decomposition kinetics of RDX in the presence of these catalysts have been evaluated with the DTG and DSC experimental data, and results show that the CuO@C and Fe2O3@C were able to reduce the Ea of RDX decomposition by 39.8 kJ mol−1 and 50.7 kJ mol−1, which is suggestive of an enhanced decomposition process for RDX by addition of carbon-loaded catalysts. The TG-FTIR analysis indicates that, in the presence of CuO@C and Fe2O3@C, the gaseous products are dominated by N2O in RDX decomposition. [ABSTRACT FROM AUTHOR]

To demonstrate the discrepancies of the international standards on compatibility evaluation for energetic additives, a comparative study on compatibility of three typical graphene-based catalysts with common energetic ingredients has been done by using DSC and VST methods. Based on some unusual findings, further suggestions are proposed on improvement in the compatibility evaluation standard. The compatibility results from DSC and VST methods for HMX/GT-Ni, HMX/GC-Cu, AP/GC-Cu, AP/GT-Ni and RDX/GC-Cu systems are contradictory. The major discrepancies between DSC and VST results are caused by combination of contradictory nature of stabilization and catalytic effects of these additives on the corresponding energetic ingredients. It has been shown that the HMX/GC-Ni, HMX/GT-Ni, AP/GT-Ni, NC/GC-Ni, NC/GT-Ni, NC/GT-Cu and NC/GA-Cu mixtures have good compatibility, and the RDX/GC-Ni, AP/GC-Ni and NC/GC-Cu mixtures have moderate compatibility. In general, the copper-based additives even under the stabilization of graphene oxide are not so compatible with nitramine oxidizers and AP. These results indicate that each of the evaluation standards on compatibility has its own feature and limitation. The DSC standard is probably not suitable for the evaluation of the compatibility of GC-Ni, GC-Cu, GT-Ni, GT-Cu and GA-Cu with energetic ingredients. The compatibility assessment cannot simply rely on the available standards, and more comprehensive evaluation procedures need to be established according to the nature of the materials evaluated. [ABSTRACT FROM AUTHOR]

In this paper, the thermal stability and decomposition kinetics of 10 nitric esters including nitroglycerine (NG), pentaerythritol tetranitrate (PETN), trimethylolethane trinitrate (TMETN), dipentaerythritol hexanitrate (DiPEHN), trimethylolpropane trinitrate (TMPTN), xylitol pentanitrate (XPN), sorbitol hexanitrate (SHN), erythritol tetranitrate (ENT), mannitol hexanitrate (MHN) and nitroisobutylglycerol trinitrate (NiBGT) are investigated by non-isothermal TG and DSC. It has been shown that the mass loss processes of NG, TMETN and TMPTN are more dependent on the heating rate, and the simultaneous evaporation makes the initial temperatures for their mass loss lower than those of the other nitric esters. Based on the correlations among their thermal stability, activation energy, detonation velocity and heat of combustion, one could conclude that the oxygen coefficient (α) plays a positive role on the decomposition heat release efficiency (ηd) when it is less than one, whereas when the α is greater than or equals to one, the fuel elements such as C and H contents would play a decisive role on ηd. It has been further proved that the order of contribution rate of function groups on the tertiary carbon to the detonation velocity could be –CH3 < –NO2 < –C2H5 < –ONO2. In addition, the introduction of function groups to the tertiary carbon is in favor of increasing the thermal stability of nitric esters due to increase in symmetry and rigidity of their molecules. The proportion numbers (Cs) of methylene group (–CH2–) to tertiary carbon or quaternary carbon will, to some extent, determine the thermal stability of the nitric esters. [ABSTRACT FROM AUTHOR]

In this paper, the thermal degradation properties of Viton A and Fluorel are investigated by both isoconversional and combined kinetic analysis methods using non-isothermal thermogravimetry technique. It has been found that the heating rate has little affect on the degradation residue of Fluorel and Viton A, where around 1.3% char was formed for Fluorel and 3.5% for Viton A. Different from the literature, the decomposition of Viton A should be considered as an overlapped dehydrofluorination and carbon chain scission process, with activation energy of 214 ± 11 and 268 ± 13 kJ mol, respectively. The effect of dehydrofluorination on degradation of Fluorel is not so significant due to low content of H, and hence, it could be considered as a single-step mechanism with average activation energy of 264 ± 14 kJ mol. The thermal stability of Fluorel is much better than that of Viton A, and the predicted half-life is around 218 min for Fluorel and 49 min for Viton A at 420 °C, which are consistent with experimental values. If using a single-step model as in the literature for Viton A, its half-life at 420 °C would be underestimated for >20%. [ABSTRACT FROM AUTHOR]

The tetrahydrate of the tetrapotassium salt of octahydroimidazo-[4,5-d]imidazol-1,3,4,6-tetrasulfonic acid (TACOS-K), an new energetic material, was investigated in terms of its crystal structure, heat of combustion, thermal stability and decomposition kinetics. Its heat of combustion is −5487 ± 96 J g from which a heat of formation of −3150 kJ mol was estimated. It has been found that this compound has a hexagonal crystal space group with a density of 2.026 g mol at 150 K. The organic anionic skeleton of the TACOS-K molecule is distinctly deformed. Six tetraanions interconnected by coordination to the potassium cations and hydrogen bridges to water molecules form hydrophilic as well as hydrophobic cavities. As an intermediate to synthesize cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole, it decomposes at around 31 °C with a first peak temperature range of 46.6-94.3 °C due to loss of water, depending on the heating rates. Hydrolysis of the N-S bonds might play an important role here. Crystalline water evaporation competes with this hydrolysis. TACOS-K has a residual mass of about 46 % at 2 °C min, which increases with the heating rate. Peak of the exothermic process occurs at 235.6 °C at the same heating rate with an enthalpy change of 164 J g. Dehydration occurs with an energy barrier of 36.7 kJ mol followed by a shoulder mass loss process with a much higher activation energy 110.6 kJ mol, while the activation energy for the main exothermic reaction is about 136.2 kJ mol. [ABSTRACT FROM AUTHOR]

Erythritol tetranitrate (butane-1,2,3,4-tetrayl tetranitrate, ETN) has become one of the most synthesized improvised explosives nowadays as it can be found on public internet discussion boards. However, the low melting point, nitrocellulose gelling ability, high energy content, and availability of its precursor make the substance potentially useful in industry as an energetic component or additive in certain gun propellants. Mixtures of ETN with other high explosives are also frequently discussed on web pages dealing with improvised explosives. This article describes thermal behavior and decomposition kinetics of pure ETN and its mixtures with pentaerythritol tetranitrate and cyclonite (1,3,5-trinitro-1,3,5-triazinane, RDX). The thermal behavior and decomposition kinetics of such mixtures are described using non-isothermal DSC and TG techniques. Kissinger method, Soviet manometric method, and modified Kissinger-Akahira-Sunose method were used for data evaluation. [ABSTRACT FROM AUTHOR]

The zero-order reaction rates (specific rate constants) for isothermal decomposition at 120 °C of plastic bonded explosives (PBXs) were measured by means of the Czech vacuum stability test, STABIL. The PBXs are based on 1,3,5-trinitro-1,3,5-triazinane (RDX), β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5- d] imidazole (BCHMX), and ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-HNIW, ε-CL-20) with 9 wt.% of the C4 type matrix, i.e., a matrix containing 25 wt.% of polyisobutylene, 59 wt.% of dioctyl sebacate and 16 wt.% of the oil HM46. Dependencies were found between the specific rate constants mentioned and the detonation velocities of the PBXs, and consequently between these constants and the impact of pure explosive fillers, i.e., RDX, β-HMX, ε-HNIW, RS-ε-HNIW, and BCHMX and, at the same time, the corresponding PBXs. The results obtained are compared with those from a recent analogous study of PBXs using an SBR (Formex P1) binder which could increase the PBXs' reactivity in comparison with C4 matrix. These results also help to dispel a widely held view about HNIW being a relatively sensitive explosive. [ABSTRACT FROM AUTHOR]

The crystal structure, thermal behavior, and decomposition kinetics of ε-CL-20, RS-ε-CL-20, α-CL-20, ε-CL-20/C4, and RS-ε-CL-20/C4 were investigated by nonisothermal FTIR, TG, and DSC techniques. It was found that the thermal decomposition of α-CL-20, ε-CL-20/C4, and RS-ε-CL-20/C4 could be considered as a two-step process and the initial step is partly controlled by crystal structure. However, the crystal structure could only affect the initial step of decomposition and the total heat release, and the heat release of RS-ε-CL-20 is the highest compared with α- and normal ε-CL-20. In addition, the activation energy of studied materials was calculated by Kissinger method and modified KAS method, which was compared with the results obtained by other researchers. It was indicated that the obtained activation energy of ε-CL-20 by Kissinger method is about 176.0 kJ mol, which is almost the same with the results from the literatures by STABIL and Noniso-TG methods. It was noticed that the crystal structure has significant effect on the initial activation energy distribution of CL-20, while in case of second stage (α = 0.30-0.85) this effect is relatively small, resulting in identical decomposition mechanism. Moreover, the kinetic compensation effects show that the studied materials could be divided into two groups, one including ε-CL-20, RS-ε-CL-20, α-CL-20, and ε-CL-20/C4 which decompose at solid state and another including ε-CL-20/Formex and RS-ε-CL-20/C4 which decompose at partial liquid state, resulting in different kinetic compensation effects. It reveals that the C4 base could affect the distribution of activation energy of ε-CL-20 and RS-ε-CL-20 in a totally different way. [ABSTRACT FROM AUTHOR]

Thermal behavior and decomposition kinetics of Formex-bonded PBXs based on some attractive cyclic nitramines, such as 1,3,5-trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). Actually, cis-1,3,4,6-tetranitrooctahy droimidazo-[4,5-d]imidazole (BCHMX) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10, 12-hexaazaisowurtzitane (CL-20), was investigated by means of nonisothermal thermogravimetry (TG) and differential scanning calorimetry (DSC). It was found that the mass loss rate of PBXs involved in this research depends greatly on heating rate and the residue of the decomposition of these PBXs decreases with the heating rate. The onset of the exotherms was noticed at 215.4, 278.7, 231.2 and 233.7 °C with the peak maximum at 235.1, 279.0, 231.2 and 233.7 °C for RDX-Formex, HMX-Formex, CL-20-Formex, and BCHMX-Formex, respectively. Their corresponding exothermic changes were 1788, 1237, 691, and 1583 J g. It was also observed that the dependence on the heating rate for onset temperatures of HMX- and BCHMX-based PBXs was almost the same due to their similar molecular structure. In addition, based on nonisothermal TG data, the kinetic parameters for thermal decomposition of these PBXs were calculated by isoconversional methods. It was shown that the Formex base has great effects on the activation energy distribution of nitramines. It was further found that the kinetic compensation effects occurred during the thermal decomposition of nitramine-based PBXs, and they almost have the same compensation effects due to similar decomposition mechanism. [ABSTRACT FROM AUTHOR]

The zero-order reaction rates (specific rate constants) of isothermal decomposition at 120 °C of plastic bonded explosives (PBXs) were measured by means of the Czech vacuum stability test, STABIL. The PBXs are based on 1,3,5-trinitro-1,3,5-triazinane (RDX), 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5- d]imidazole (BCHMX), and ε 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-HNIW, ε-CL-20) with 13 wt% of the Formex P1 type matrix, i.e., a matrix of the explosive with pentaerythritol tetranitrate (PETN) bound by 13 wt% of a mixture of 25 wt% of styrene-butadiene rubber and 75 wt% of an oily material. Dependencies were found between the specific rate constants mentioned and the detonation velocities of PBXs, and consequently between these constants and the impact and electric spark sensitivities of pure explosive fillers, i.e., RDX, HMX, HNIW, BCHMX, and PETN. It is stated that the higher impact or electric spark sensitivity of their pure explosive fillers corresponds to the higher thermal reactivity of the given PBXs. [ABSTRACT FROM AUTHOR]